Audio information such as that representing a musical performance or the like is often recorded to a recording medium for subsequent reproduction in a listening area via an appropriate audio reproduction system. Upon playback, it is often desired that the reproduced sound have an enhanced or lifelike aural quality which gives a listener of the reproduced sound the perception of an original performance. To attain this enhanced aural quality upon playback, multi-channel audio systems are a frequent choice for reproducing recorded audio information since multichannel systems lend themselves to providing greater definition of a perceived "sound stage" or audio "image" upon reproduction. Sound staging and imaging generally refer to the apparent soundstage from which the reproduced sound is perceived to emanate.
In order to take full advantage of the benefits which a multi-channel reproduction system provides in defining a lifelike aural quality upon playback of an audio signal, it is commonly beneficial to process the audio signals prior to being recorded onto the recording medium so that individual sounds can be reproduced within the sound stage in such a way that their position and relative size within the sound stage can be more fully defined. To accomplish this, audio control devices commonly referred to as "imaging controls", "imagers" or "wideness controls" are utilized during the process of recording, or mixing down, audio information. These imaging controls are often incorporated into audio mixing consoles utilized in the recording/mixdown process, or in portable recording equipment, and are used to vary or control the stereo base or image mode of the audio signal. In stereo audio systems, examples of image modes include, for example, "stereo" mode, "reverse stereo" mode, "wide", "reverse wide" mode, "left" mode, "right" mode and "mono", or "monaural", mode. Depending upon the image mode selected, the imaging control will provide for an appropriate level an audio signal to be recorded across each of one or more recording channels of a recording medium, with phase characteristics appropriate for achieving the desired imaging mode effect upon reproduction.
An audio mixing console may include an imaging control for processing the audio signals assigned to each particular audio channel thereof. These imaging controls are generally selectably engagable, or otherwise insertable into the signal path of the audio mixing console, by the operator of the mixing console through manipulation of one or more control elements, such as switches or potentiometers. In general, it is advantageous for an audio imaging controller to provide a multiple number of imaging modes for processing an audio signal. Further, to avoid complicating the recording process for the operator of the mixing console, it is advantageous to have a minimal number of control elements which must be manually manipulated to attain the desired results.
Examples of currently available image control devices include imaging controls such as those incorporated into the AMEK BCIII or Classic, the NEVE 55 Series, or the Solid State Logic SL-5000M Series mixing consoles. These types of imaging controllers vary in the capabilities and features which they provide. For example, some imaging controls such as the AMEK BCIII, allow a user to vary the image mode of the audio signal from a "stereo" mode to a "mono" mode to a left/right "reversed stereo" mode through manipulation of a single control element, such as a potentiometer. Others, such as the Solid State Logic SL-5000M series, allow for the audio signal image mode to be varied from "stereo" to "mono" to a "reverse" stereo through manipulation of a rotary control element and a separate width control button. Others allow the audio image mode to be varied from a "left/right" to "mono" to "right/left" through manipulation of a single control element. Although these types of image controllers allow the image quality or characteristics to be altered to produce a desired result upon reproduction, those that can be operated through manipulation of a single control element are limited in the number of imaging modes they can provide. Those that can provide a more extensive number of attainable image modes, unfortunately, generally require an operator to manipulate more than one control element. Aside from the disadvantage of having to deal with more than one control element, these additional control elements increase the cost associated with the production of the image controller.
Another type of imaging control device is described in a U.S. patent application entitled Stereo Image Control Circuit which was filed on Feb. 25, 1994. Ser. No. 08/202,029 (Attorney of Record: Ronald P. Kananen; Docket No.: S0A-053; Inventor(s): J. Dombrowski and B. Orozov). This application is assigned to the assignee of the present invention and is hereby incorporated herein by reference. This type of image controller allows the image mode of an audio signal to be varied over multiple image modes by manipulating a single control element, such as a rotary potentiometer. In this manner, the image mode of a stereo audio signal can be varied as desired over a range of image modes from "wide" to "stereo" to "mono". FIG. 1 shows a schematic diagram of this type of image controller. While this type of imaging control device provides the clear advantage of multiple image modes and easy use via a single control element, it also uses substantial circuitry and components, such as resisters 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 and 24; potentiometers 25, 26, 27 and 28; and operational amplifiers 29, 30, 31, 32, 33 and 34, to implement.